Electrospray ionization (ESI) mass spectrometry (MS), or ESI-MS, has become a vital tool in biological research. Central to ESI-MS is the manipulation, transmission, and increasingly the trapping of ion populations. In a population of ions, electric fields of the ions influence each other and the collective effect is known as space charge. The detrimental effects of excessive space charge on instrumental performance are well known in the art. For example, like-charged ions repel each other, and the electric field of an ion cloud distorts the electric fields from the elements, optics, and mass analyzer of the mass spectrometer. Further, space charge reduces the mass measurement accuracy in various instruments, including, e.g., Fourier transform ion cyclotron resonance (FTICR) MS. Similarly, 3-D ion traps suffer from detrimental effects from excessive space charge which leads to shifts in secular frequencies, changes in optimal excitation amplitudes, and plasma effects. Space charge can also cause radial stratification of ions and unwanted fragmentation in accumulation quadrupoles or multipoles in general. Various strategies and techniques have been employed in an attempt to reduce the influence of space charge, including, e.g., data-dependent corrections and calibrations and automated methods which regulate and decrease the variation of ion populations in a mass analyzer. However, data-dependent corrections and calibrations do not reduce or eliminate space-charge effects. Further, such approaches are limited in that they cannot distinguish ions of interest from those that constitute background ions.
Accordingly, there remains a need for methods and devices that significantly reduce and/or eliminate space-charge effects in analytical instruments and related components or systems thereby improving analysis results.